Prof. Rijke on some Properties of the Induced Current, 259 



nature to raise many doubts on this subject. I therefore resolved 

 to make some experiments to ascertain on what I conld rely, 

 and I found that the deviations of the dynamometer do not change 

 ichen the inducing current is broken between the poles of an electro- 

 magnet. 



12. We have seen on what considerations we depend when 

 we desire to prove that whatever tends to increase the striking 

 distance of the induced current, ought also to tend to increase 

 the deflection which this ^current produces in a dynamometer. 

 "V\ e know that by analogous reasonings it is thought to be shown 

 that the physiological effect of the induced current, as well as the 

 thermal action which it exerts on a metallic wire, ou°;kt both to 

 increase when the rupture of the inducing circuit is effected 

 under circumstances favourable to the increase of the striking 

 distance. But having seen that the deflections of the dynamo- 

 meter do not necessarily depend on the circumstances which 

 favour the striking distance of the induced current, I concluded 

 it was very possible that the physiological and thermal effects 

 were also independent, and that it was for experiment to decide. 



To investigate the physiological effect, I employed a small-sized 

 RuhinkorfFs coil. Although I only used a single DanielFs 

 element, yet to render the shock bearable it was necessary to 

 withdraw almost completely the bundle of iron wires. But far 

 from the shock becoming stronger, I found constantly that it 

 diminished in intensity when the rupture took place in a coal- 

 gas flame. I obtained the same results by working with another 

 and less powerful induction coil, and in which I could intro- 

 duce a greater extent of bundle of iron wire. 



An electrical thermometer, constructed according to the plan 

 of M, Riess, served to compare the thermal effects which the 

 induced current produces when the rupture of the inducing 

 circuit takes place successively in air and in the middle of a 

 flame. The apparatus was arranged so as to render it as sensi- 

 tive as possible. It is almost unnecessary to add that the two 

 ends of the platinum wire with which the apparatus is furnished 

 were in metallic connexion with the two ends of an induced helix. 

 I commenced by using a RuhmkorfPs apparatus, but I soon saw 

 that the induced current was without action on the electro- 

 thermometer, and that I should only succeed by using an appa- 

 ratus in which the induced wire did not offer such a conside- 

 rable resistance. I obtained satisfactory results, although the heat 

 developed in the platinum wire was inconsiderable, by making 

 use of an electro-magnet which I employ for experiments on dia- 

 magnetism, and which was constructed according to RuhmkorfFs 

 plan (Daguin, Traite de Physique, 2nd edit. vol. hi. p. 749). Each 

 of the bobbins consists of three copperwires, one of which served as 



